The present invention relates to a system for controlling the concentration of toner within the developer mixture in a xerographic printer.
In the well-known process of electrostatographic printing, also known as xe2x80x9cxerography,xe2x80x9d a charge retentive surface, typically known as a photoreceptor, is electrostatically charged, and then exposed to a light pattern of an original image to selectively discharge the surface in accordance therewith. The resulting pattern of charged and discharged areas on the photoreceptor form an electrostatic charge pattern, known as a latent image, conforming to the original image. The latent image is developed by contacting it with a finally divided electrostatically attractable powder known as xe2x80x9ctoner.xe2x80x9d Toner is held on the image areas by the electrostatic charge on the photoreceptor surface. Thus, a toner image is produced in conformity with a light image of the original being reproduced. The toner image may then be transferred to a substrate, such as paper, and the image affixed thereto to form a permanent record of the image to be reproduced.
The step in the electrophotographic process in which the toner is applied to the latent image is known as xe2x80x9cdevelopment.xe2x80x9d In any development system, a quantity of toner is brought generally into contact, with the latent image, so that the toner particles will adhere or not adhere to various areas on the surface in conformity with the latent image. Many techniques for carrying out this development are known in the art. A number of such techniques require that the toner particles be evenly mixed with a quantity of xe2x80x9ccarrier.xe2x80x9d Generally speaking, toner plus carrier equals xe2x80x9cdeveloper.xe2x80x9d Typically, toner particles are extremely fine, and responsive to electric fields; carrier particles are relatively large and respond to magnetic fields. In a xe2x80x9cmagnetic brushxe2x80x9d development system, the developer is exposed to relatively strong magnetic fields, causing the carrier particles to form brush-like strands, much in the manner of iron filings when exposed to a magnetic field. The toner particles, in turn, are triboelectrically adhered to the carrier particles in the strands. What is thus formed is a brush of magnetic particles with toner particles adhering to the strands of the brush. This brush can be brought in contact with the latent image, and under certain conditions the toner particles will separate from the carrier particles and adhere as necessary to the photoreceptor.
An important process parameter for any development system is the ratio of toner particles to carrier within the developer. It is also expectable that, in the course of use of the printer, the toner to carrier ratio (T/C) will change significantly as toner particles are transferred from the developer supply to the photoreceptor and ultimately to print sheets. There have thus been numerous systems devised in the prior art for determining and controlling this T/C in an operating machine. Because carrier particles are generally heavy and magnetic, while toner particles are generally light and non-magnetic, many of these systems involve detecting the behavior of magnetic flux through the developer; placing a quantity of developer between capacitor plates and examining the electrical behavior thereof; or electrically drawing a quantity of toner from the developer and inferring a T/C therefrom. However, very often such systems have proven to be either inaccurate, imprecise, or too expensive for use in inexpensive printers and copiers.
The present invention is directed to a highly precise system for monitoring and controlling the T/C in a developer supply.
U.S. Pat. No. 4,614,165 discloses the general concept of using a secondary developer supply for gradually admixing fresh developer into a primary developer supply, thereby retaining a reasonably constant T/C in the primary developer supply.
U.S. Pat. No. 5,204,698 discloses the concept of counting developed pixels in image data, and relating the pixel count to a determination of when toner should be dispensed into a primary developer supply.
U.S. Pat. No. 5,390,004 discloses a control system for a xerographic printing system in which the reflectivity of a set of test patches is measured, and the reflectivities are fed into a fuzzy-logic control system for the xerographic parameters.
U.S. Pat. No. 5,402,214 discloses a control system for a xerographic printing system in which the reflectivity of a test patch is measured, and the DC bias of a field associated with the development unit is adjusted accordingly. When the DC bias is caused to exceed a predetermined maximum, fresh developer is added to the primary developer supply.
U.S. Pat. No. 6,035,152 discloses a control system for a xerographic printing system in which the reflectivity of a set of test patches is measured, and the reflectivities are fed into a control system for the xerographic parameters.
According to one aspect of the present invention, there is provided an electrostatographic printing system in which there is provided a primary supply of developer material, the developer material comprising toner and carrier, wherein the developer material in the primary supply is used for developing electrostatic latent images on a charge receptor, a secondary supply of developer material, and dispense means for conveying developer material from the secondary supply to the primary supply. A control method comprises the steps of monitoring a dispense rate of toner being used to develop electrostatic latent images, thereby determining a pixel dispense in substantially real time; monitoring a ratio of toner to carrier (T/C) in the primary supply, thereby determining a T/C dispense in substantially real time; and developing a test patch with the developer material, the test patch being of a predetermined target reflectivity, and monitoring an actual reflectivity of the test patch, thereby determining a patch dispense in substantially real time. The dispense means is controlled according to an algorithm which takes into account the pixel dispense, the T/C dispense, and the patch dispense.
According to another aspect of the present invention, there is provided an electrostatographic printing system in which there is provided a primary supply of developer material, the developer material comprising toner and carrier, wherein the developer material in the primary supply is used for developing electrostatic latent images on a charge receptor, a secondary supply of developer material, and dispense means for conveying developer material from the secondary supply to the primary supply. At least one behavior of the system is monitored. In an algorithm, the monitored behavior is expressed as an amount of time for the dispense means to convey developer material. The dispense means conveys developer material from the secondary supply to the primary supply in response to accumulating a predetermined amount of time for the dispense means to convey developer material.